The present invention relates generally to inductive charging systems and, more particularly, to an inductive charging system and improved fluid-cooled transformer coil and transmission cable for use therein.
The assignee of the present invention designs and develops electric vehicles and electric vehicle charging systems. For reference purposes, U.S. Pat. No. 5,684,380 entitled xe2x80x9cOil Cooled High Power Inductive Couplerxe2x80x9d assigned to the assignee of the present invention discloses an inductive coupler for use in electric vehicle charging systems.
In an electric vehicle charging system, heat dissipation increases in relation to the square of the current being transferred to the electric vehicle. As power increases, the amount of heat produced in the power electronics package, cable and coupler becomes significant. The coupler alone dissipates in excess of 180 watts over a 20 square inch area (surface area approximately equivalent to the palm size of an adult human hand). In an unmanaged situation, such heat flux leads to unacceptable touch temperature profiles for the cable and coupler. An appropriate thermal management system is essential to add practicality, reliability and efficiency throughout the entire inductive charging system.
There is sufficient accumulated analysis and experience with inductive charging systems previously developed by the assignee of the present invention to determine the disadvantages encountered if its rate of charge is increased. The most obvious disadvantages are an increase on physical size and a limited rate of charge of the electric vehicle. These restrictions are dictated by the amount of heat produced and the fact that the system relies on heat conduction, via liquid to air heat and/or air to air heat exchangers.
This approach limits the system, and the system must provide cooling to slightly above ambient and charge rates are below level 1, which is below 1.44 kW. If charge rates larger than this value are required, the physical size of heat exchangers and fans will be prohibitive as power dissipation increases throughout the system, including the electronic package, cable and coupler. Furthermore, the noise created by a fan or blowers will be substantially increased as more air is forced through the system.
Therefore, it would be desirable to have a liquid-cooled inductive charging system that enhances the cooling efficiency of the entire system and maintains touch temperatures of user interface components (cable and coupler) well within acceptable limits. It would be desirable to have an improved multilevel helix, spiral fluid-cooled transformer coil that improves the heat dissipating capability of inductive charging systems, such as electric vehicle charging systems, and the like. It would also be desirable to have an improved fluid-cooled transmission cable that improves the heat dissipating capability of inductive charging systems, such as electric vehicle charging systems, and the like.
The present invention provides for an improved inductive charging system, fluid-cooled transformer coil, and fluid-cooled transmission cable for use in charging electric vehicle battery packs. An exemplary embodiment of the inductive charging system comprises a power source, cooling fluid pumping and cooling apparatus and a charge port, such as may be disposed in an electric vehicle that is coupled to batteries thereof. The charge port comprises a secondary winding of the charging system. A high power fluid-cooled inductive charging coupler that is insertable into the charge port to couple power from the power source to charge the batteries of the electric vehicle is provided. The inductive charging coupler comprises a housing, a ferrite puck, and an insulated, liquid-cooled, current-carrying conductive tubular transformer coil disposed around the ferrite puck that forms a primary winding of the charging system. A liquid-cooled, liquid-carrying tubular transmission cable is coupled to the power source, to the cooling fluid pumping and cooling apparatus, and to the tubular transformer coil, that couples current thereto from the power source, and couples cooling fluid thereto.
An exemplary embodiment of the transformer coil is a multilevel helix, spiral fluid-cooled transformer coil that comprises an eight turn (although n turns are possible), two level helix, four turn spiral winding, comprising an insulated tube high current carrying capacity conductor that optimizes AC and high frequency losses. Level 2 (6.66 kW) charging systems may readily utilize this primary winding without requiring liquid cooling. The same primary winding may be used with liquid cooling for Level 3 charging greater than 7.68 kW. The present invention reduces the size, volume and operating temperature of the charging system while increasing the power density and reliability of the system.
The inductive charging system operates in a fast and efficient manner while maintaining the touch temperature of user interface components of the system well within acceptable limits. The transformer coil may be advantageously used in an off-board inductive charger system and may also be incorporated in an onboard charging system (charge port) using a compact closed loop system installed/modified existing cooling system on an electric vehicle.
The multilevel helix, spiral fluid-cooled transformer coil may be readily employed when a super fast rate of charging the battery pack that powers electrically-powered vehicles is desired. Also, the present invention provides for a more compact design without causing thermal runaway or compromising power density.